High naphthenic acid and asphaltene content crude oils possess the tendency to form stable emulsions of the water-in-crude oil and crude oil-in-water type. The polar naphthenic acids and asphaltenes in the crude oil stabilize dispersed water droplets in water-in-oil emulsions and the oil droplets in oil-in-water emulsions. Further, sub-micron size solids like silica and clay, when present in the crude oil, interact with the polar acids and asphaltenes and enhance the stability of the emulsions formed. Formation of stable water-in-crude oil and crude oil-in-water emulsions result in difficulty in separation of water and crude oil. The problem is faced both at production facilities and in refinery desalters.
Electrostatic demulsification in the presence of chemical demulsifiers is the most widely used technology for demulsification of water-in-crude oil emulsions. Gravity settling and centrifugation in conjunction with chemical demulsifiers are employed for water-in-oil and oil-in-water emulsions. Recently, a microwave technology (See for example U.S. Pat. Nos. 6,086,830 and 6,077,400) patented by Imperial Petroleum Recovery Corporation has emerged for treatment of hard to treat emulsions especially the rag layer. Thermal flash methods are also known in the art.